1. Technical Field of the Invention
The present invention relates to an apparatus for reading a disk, such as CD-ROM, CD-R, DVD-ROM, DVD-RAM, etc., in which digital data have been recorded in a spiral track, and particularly relates to a disk reading apparatus by which the rotary speed of the disk is lowered when vibration is generated due to eccentric center of gravity of the disk.
2. Background of the Related Art
In a disk reading apparatus for reading data from a CD-ROM, in order to shorten the time taken to read data, the CD-ROM is rotated to read the data at a speed higher than a normal speed, for example, at a 8-fold speed, a 16-fold speed, or the like. On the other hand, the specification regarding the eccentric center of gravity of the CD-ROM is set to a value which causes no problem in reading data in the condition that the CD-ROM is rotated at the normal speed. Therefore, when the CD-ROM is rotated at a speed higher than the normal speed, there may be a case where the eccentric center of gravity becomes strongly influential to increase the quantity of vibration to thereby cause a difficulty in data-reading. In the case where a CD-ROM is rotated at a high speed, therefore, it is detected whether vibration is generated or not so that the rotary speed can be lowered to read data when vibration is detected.
To this end, conventionally, Unexamined Japanese Patent Publication No. Hei-4-143928 has proposed a technique in which whether vibration is generated or not is detected when a disk is rotated. That is, in this technique, mechanical vibration of a rotation driving section for rotating a disk is detected by means of a sensor. The output of the sensor is fed to a band-pass filter, while the frequency of the band-pass filter is set to a frequency corresponding to the rotary speed of the disk. Accordingly, only a frequency component corresponding to the rotary speed of the disk is outputted from the band-pass filter. The signal outputted from the band-pass filter is led to a window comparator in which the signal is binarized and supplied to the external section as an abnormal detection signal.
When the above-mentioned configuration is adopted, however, a problem had arisen as follows. That is, when an external impact was given to the reader, strong vibration was generated in the reading apparatus. This strong vibration was detected by the sensor. On the other hand, the attenuation property of the band-pass filter became comparatively gentle so as to be about 6 dB/octave when the circuit configuration was simplified. Therefore, when a frequency component near the pass frequency of the band-pass filter was included in the output of the sensor detecting the vibration caused by the impact, an abnormal detection signal was outputted due to the impact. Therefore, in a situation where a portion of a human body or the like hit against a desk on which the reading apparatus was located to give an impact to the apparatus, an abnormal detection signal was sent out. Accordingly, notwithstanding the capability of being read at a high rotary speed, the disk was read at a low rotary speed so that the reading speed was thus lowered.